The heretic's fork was a torture device, loosely consisting of a length of metal with two opposed bi-pronged "forks" as well as an attached belt or strap.[1]
The device was placed between the breast bone and throat just under the chin and secured with a leather strap around the neck, while the victim was hung from the ceiling or otherwise suspended in a way so that they could not lie down.[2] A person wearing it couldn't fall asleep. The moment their head dropped with fatigue, the prongs pierced their throat or chest, causing great pain.[1][3] This very simple instrument created long periods of sleep deprivation. People were awake for days, which made confessions more likely.[1]
Traditionally, the fork was engraved with the Latin word abiuro (meaning "I recant"), and was used by the various Inquisitions.[4]